1. Field of the Invention
The present invention is directed to a process and a device for threading elongated metal workpieces, in particular pipes or tubes, into a drawing apparatus for cross-sectional reduction in more than one drawing step by means of at least two successive drawing units which grasp the workpiece at the outer circumference and have revolving chains which draw the workpiece continuously through a drawing ring associated with each drawing unit and arranged in a drawing ring holder.
2. Description of the Related Art
Continuous drawing machines are well known and are used, preferably for copper pipes or tubes, with two alternately acting drawing sledges, as for example disclosed in European Patent publication 0182922, or a chain-type drawing machine such as that disclosed in European Patent publication 0548723.
In order to initiate the drawing process, it is conventional in the prior art to draw out the pointed beginning of the tube, also referred to as the "point", in a plurality of steps until the actual drawing devices are capable of fully grasping the tube with the clamping jaws of the first drawing carriage or with the chains of the first chain-type drawing machine in order to be able to apply the drawing force to the tube. For example, European Patent Application 0645200 describes a device by means of which the tube is predrawn on the first piece, that is, its wall and diameter are reduced, whereby the beginning of the tube is fed by the appropriate length to the revolving chains, so that these chains grasp the tube along their entire length already during the initial drawing. Naturally, this process entails time losses and represents a clear limitation of the productive capacity of conventional continuous drawing machines. Further, prior art continuous drawing machines must be provided with auxiliary devices which are used within the cycle for drawing a tube and thus, not only complicate the plant or installation, and as a result make it more expensive, but also impede productive capacity.
The object of the present invention, therefore, is to provide a process and a device in which the duration of the threading process associated with the method and the duration of the predrawing of the tubes is substantially reduced with relatively little, if any, reduction in the drawing speed of the drawing units.